A fuel injection system (10) with reduced pressure pulsations in the fuel discharge paths from the injectors is disclosed. A high-pressure fuel accumulated in a common rail is injected by a plurality of the injectors. Each injector includes a high-pressure chamber for accumulating the fuel, a back pressure chamber into which the high-pressure fuel is introduced from the high-pressure chamber and a nozzle body arranged in the high pressure chamber. Each injector closes the fuel injection port by pushing down the nozzle body under the pressure of the high-pressure fuel introduced into the back pressure chamber. The fuel injection port is opened, on the other hand, by discharging the high-pressure fuel from the back pressure chamber through the fuel discharge path of each injector. A variable-area orifice (6) is arranged in the discharge path (55) downstream of the confluence at which all the fuel discharge paths from the injectors are merged with each other. The higher the fuel pressure in the discharge paths, the larger the open area of the variable-area orifice. Thus, a pressure pulsation in the fuel discharge paths from the injectors is reduced.
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1. A fuel injection system of an internal combustion engine for injecting a high-pressure fuel accumulated in a common rail from a plurality of injectors,
wherein each of said injectors includes a high-pressure chamber for accumulating the fuel, a back pressure chamber into which the high-pressure fuel in said high-pressure chamber is introduced and a nozzle body arranged in said high pressure chamber,
wherein said injector closes the fuel injection port by pushing down said nozzle body under the pressure of the high-pressure fuel introduced into said back pressure chamber on the one hand and said high-pressure fuel in said back pressure chamber is discharged through the fuel discharge path of said injector thereby to open said fuel injection port on the other hand,
wherein a variable-area orifice is arranged in a common discharge path downstream of the confluences of all the fuel discharge paths from the injectors, and
wherein an open area of said variable-area orifice is increased in response to an increase in fuel pressure in said common discharge path.
2. A fuel injection system of an internal combustion engine according to
wherein the open area of said variable-area orifices are increased with the increase in fuel pressure in the fuel discharge paths.
3. A fuel injection system of an internal combustion engine according to
wherein said variable-area orifice is formed of a first chamber communicating with said injectors and a second chamber integrated with said first chamber and including an outlet,
wherein said variable-area orifice includes a sliding member adapted to slide along the inner wall of said first chamber, and at least one communication hole is formed in the sliding surface of said sliding member for establishing communication between said first chamber and said second chamber at the time of sliding of said sliding member,
wherein said variable-area orifice includes an urging means to urge the sliding means away from the second chamber,
and wherein the open area of said communication hole is increased when said sliding member slides toward said second chamber under the pressure of the fuel in said fuel discharge path against the force of said urging means.
4. A fuel injection system of an internal combustion engine according to
wherein a plurality of communication holes are formed to establish communication between the first chamber and the second chamber, said communication holes in the sliding surface of said sliding member being each in the shape of circle, and
wherein the inner edge of at least one of said plurality of the communication holes in the sliding surface of said sliding member and the outer edge of an adjacent communication hole in the sliding surface of said sliding member are located at substantially the same position in the sliding direction in which said sliding member slides.
5. A fuel injection system of an internal combustion engine according to
wherein said communication hole is at least a slit extending in the sliding direction.
6. A fuel injection system of an internal combustion engine according to
wherein the increasing rate of the open area of each communication hole increases with an increase the sliding distance of said sliding member.
7. A fuel injection system of an internal combustion engine according to
wherein the open area of said variable-area orifice is changed by at least one of the number, shape and size of said communication holes formed in the sliding surface of said sliding member.
8. A fuel injection system of an internal combustion engine according to
wherein said variable-area orifice is formed of a first chamber communicating said injectors and a second chamber integrated with said first chamber and including an outlet, said variable-area orifice includes a sliding member adapted to slide along the inner wall of said first chamber, at least one of the inner wall of said first chamber and the sliding surface of said sliding member is tapered, and said variable-area orifice includes an urging means to urge the sliding means away from the second chamber, and
wherein when said sliding member slides toward said second chamber under the pressure of the fuel in said fuel discharge path against the force of said urging means, the clearance between the inner wall of said first chamber and the sliding surface of said sliding member is increased.
9. A fuel injection system of an internal combustion engine according to
wherein said second chamber is larger than said first chamber, and said sliding member includes a flange adapted to sealably abut the step between said first chamber and said second chamber.
10. A fuel injection system of an internal combustion engine according to
wherein said sliding member of said variable-area orifice is controlled by a drive member.
11. A fuel injection system of an internal combustion engine according to
wherein said variable-area orifice is formed of a first chamber communicating with said injectors and a second chamber integrated with said first chamber and including an outlet,
wherein said variable-area orifice includes a sliding member adapted to slide along the inner wall of said first chamber, and at least one communication hole of a communication passage is formed in the inner wall of said first chamber for establishing communication between said first chamber and said second chamber at the time of sliding of said sliding member,
wherein said variable-area orifice includes an urging means to urge the sliding means away from the second chamber,
and wherein the open area of said communication hole is increased when said sliding member slides toward said second chamber under the pressure of the fuel in said fuel discharge path against the force of said urging means.
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1. Field of the Invention
The present invention relates to a fuel injection system or, in particular, to a fuel injection system employed in a diesel engine.
2. Description of the Related Art
Generally, an accumulator (common-rail) fuel injection system has such a configuration that high-pressure fuel, supplied from a high-pressure chamber, is introduced into a control chamber arranged in a fuel injection valve and a nozzle body is lowered to maintain a fuel injection port in closed state. Further, the fuel in the control chamber is allowed to leak into fuel discharge paths so that the internal pressure of the control chamber is reduced thereby to raise the nozzle body, with the result that the fuel injection port is opened to inject the fuel (see, for example, Japanese Unexamined Patent Publications. Nos. 2003-021017, 11-022580, 11-022583 and 11-022584).
In order to inject a predetermined amount of fuel within a short time, the fuel in the control chamber must be discharged in one operation into the fuel discharge paths at the sacrifice of a pressure pulsation caused in the fuel discharge paths. Normally, a check valve is arranged in the discharge path downstream of each injector, and a pressure pulsation may be caused also by the operation of a check valve. A sustained pressure pulsation in the fuel discharge paths will change the force acting on the control valve, etc. and adversely affects the operation of the nozzle body, thereby changing the amount of fuel injected.
Especially in the case where the interval is short between one injection and another, the fuel may be injected during a large pressure pulsation caused, in the fuel discharge path, by the preceding injection. In such a case, if the time when the pressure in the fuel discharge path drops coincides with the injection timing of the injector, the force acting on the control valve is reduced and the control valve lifts at a higher rate, and the fuel is rapidly discharged from the control chamber. Thus, the nozzle body rises rapidly, often resulting in the injected fuel amount being increased beyond the desired amount. In the case where the time when the internal pressure of the fuel discharge path rises coincides with the injection timing of the injector, on the contrary, the amount of fuel injected is liable to be smaller than required.
Further, the recent trend toward the employment of a pilot injection before the main injection and a post injection after the main injection has further shortened the interval between injections. This increases the possibility of frequent changes or variations in the amount of fuel injected. Also, an increased pressure pulsation in each fuel discharge path is accompanied by frequent cavitation and promotes the erosion of the actuator chamber of the actuator for controlling the control valve, thereby leading to a shorter service life of the parts. Although the pressure pulsation is attenuated by a longer distance, of the fuel discharge path, between the injectors, the recent demand for a smaller fuel injection system makes it difficult to shorten the distance of each fuel discharge path between the injectors to such a degree as to completely attenuate the pressure pulsation.
This invention has been achieved in view of this situation, and the object thereof is to provide a fuel injection system, for an internal combustion engine, in which the pressure pulsation in the fuel discharge paths from the injectors is reduced while, at the same time, suppressing the variations in the amount of fuel injected from each injector.
In order to achieve the object described above, according to a first aspect of the invention, there is provided a fuel injection system, for an internal combustion engine, for injecting a high-pressure fuel accumulated in a common rail from a plurality of injectors, wherein each of the injectors includes a high-pressure chamber for accumulating the fuel, a back pressure chamber into which the high-pressure fuel in the high-pressure chamber is introduced and a nozzle body arranged in the high pressure chamber, wherein the injector closes the fuel injection port by pushing down the nozzle body under the pressure of the high-pressure fuel introduced into the back pressure chamber, on the one hand, and the high-pressure fuel in the back pressure chamber is discharged through the fuel discharge path of the injector thereby to open the fuel injection port, on the other hand, wherein a variable-area orifice is arranged in a common discharge path downstream of the confluence of all the fuel discharge paths from the injectors, and wherein the open area of the variable-area orifice is increased with an increase in fuel pressure in the common discharge path.
In the first aspect of the invention, the open area of the variable-area orifice is changed by the fuel pressure. Unlike in the prior art using a check valve, therefore, the fuel is prevented from being discharged in one operation and therefore the pressure in the common discharge path does not undergo a sudden change. As a result, the pressure pulsation in the discharge paths is reduced when the high-pressure fuel is discharged from the control chamber, and the amount of the fuel injected from each injector can be stabilized.
According to a second aspect of the invention, there is provided a fuel injection system, for an internal combustion engine in the first aspect of the invention, further comprising a variable-area orifice arranged in each of the fuel discharge paths from the injectors wherein the open areas of the variable-area orifices are increased with an increase in fuel pressure in the fuel discharge paths.
Specifically, in the second aspect of the invention, the pressure pulsation in the common fuel discharge path caused at the time of fuel injection by a given injector can be prevented from being transmitted to an adjacent injector, and therefore the change in the amount of fuel injected by the injectors can be further suppressed.
According to a third aspect of the invention, there is provided a fuel injection system, of an internal combustion engine in the first or second aspect of the invention, wherein the variable-area orifice is formed of a first chamber communicating with the injectors and a second chamber integrated with the first chamber and including an outlet, wherein the variable-area orifice includes a sliding member adapted to slide along the inner wall of the first chamber, and at least one communication hole is formed in the sliding surface of the sliding member for establishing communication between the first chamber and the second chamber at the time of sliding of the sliding member, wherein said variable-area orifice includes an urging means to urge the sliding means away from the second chamber, and wherein the open area of the communication hole is increased when the sliding member slides toward the second chamber, under the pressure of the fuel in the fuel discharge path, against the force of the urging means.
Specifically, in the third aspect of the invention, the open area of the variable-area orifice is gradually increased in accordance with the sliding distance of the sliding member, and therefore the pressure pulsation can be easily reduced.
According to a fourth aspect of the invention, there is provided a fuel injection system for an internal combustion engine in the third aspect of the invention, wherein a plurality of communication holes are formed to establish communication between the first chamber and the second chamber, the communication holes in the sliding surface of said sliding member each being in the shape of circle, and wherein the inner edge of at least one of the plurality of the communication holes in the sliding surface of said sliding member and the outer edge of an adjacent communication hole in the sliding surface of the sliding member are located at substantially the same position in the sliding direction in which the sliding member slides.
Specifically, in the fourth aspect of the invention, as the communication holes in the sliding surface of the sliding member are circular in shape, the communication holes can be easily formed, and the open area of the variable-area orifice can be continuously increased when the sliding member slides, thereby making it possible to prevent hunting.
According to a fifth aspect of the invention, there is provided a fuel injection system, for an internal combustion engine in the third aspect of the invention, wherein the communication hole is at least a slit extending in the sliding direction.
Specifically, in the fifth aspect of the invention, the communication hole can be formed by only one machining operation and therefore can be formed in a short time.
According to a sixth aspect of the invention, there is provided a fuel injection system, for an internal combustion engine in any one of the third to fifth aspects of the invention, wherein the increasing rate of the open area of each communication hole increases with an increase in the sliding distance of the sliding member.
Specifically, in the sixth aspect of the invention, even in the case where the open area of the variable-area orifice is substantially a maximum, the sliding member can be slid in stable fashion in the first chamber. Also, the shortened sliding distance of the sliding member can rapidly deal with a sharp pressure increase which may occur, while at the same time reducing the size of the variable-area orifice as a whole.
According to a seventh aspect of the invention, there is provided a fuel injection system, for an internal combustion engine in the third aspect of the invention, wherein the open area of the variable-area orifice is changed by at least one of the number, shape and size of the communication holes formed in the sliding surface of the sliding member.
Specifically, the seventh aspect of the invention can produce the same functions and effects as the aforementioned aspects.
According to an eighth aspect of the invention, there is provided a fuel injection system, for an internal combustion engine in the first or second aspect of the invention, wherein the variable-area orifice is formed of a first chamber communicating the injectors and a second chamber integrated with the first chamber and including an outlet, the variable-area orifice includes a sliding member adapted to slide along the inner wall of the first chamber, at least one of the inner wall of the first chamber and the sliding surface of the sliding member is tapered, and said variable-area orifice includes an urging means to urge the sliding means away from the second chamber, and wherein when the sliding member slides toward the second chamber under the pressure of the fuel in the fuel discharge path against the force of the urging means, the clearance between the inner wall of the first chamber and the sliding surface of the sliding member is increased.
Specifically, in the eighth aspect of the invention, the clearance between the sliding member and the inner wall of the first chamber, i.e. the open area of the variable-area orifice is adapted to increase gradually in accordance with the sliding distance of the sliding member and, therefore, the pressure pulsation can be easily reduced.
According to a ninth aspect of the invention, there is provided a fuel injection system, for an internal combustion engine in any one of the third to eighth aspects of the invention, wherein the second chamber is larger than the first chamber, and the sliding member includes a flange adapted to sealably abut the step between the first chamber and the second chamber.
Specifically, in the ninth aspect of the invention, the first chamber and the second chamber can be substantially sealed as long as the flange is in engagement with the step. In the case where the fuel pressure in each fuel discharge path is lower than a predetermined value, during the assembly in the factory or a shortage of gasoline, the fuel is prevented from leaking and, at the same time, the fuel pressure quickly increases to a predetermined level.
According to a tenth aspect of the invention, there is provided a fuel injection system, for an internal combustion engine in any one of the third to ninth aspects of the invention, wherein the sliding member of the variable-area orifice is controlled by a drive member.
Specifically, in the tenth aspect of the invention, the position of the sliding member can be controlled very accurately. The drive member may be an electromagnetic solenoid or a piezoelectric actuator.
According to a eleventh aspect of the invention, there is provided a fuel injection system for an internal engine in the first or second aspect of the invention, wherein said variable-area orifice is formed of a first chamber communicating with said injectors and a second chamber integrated with said first chamber and including an outlet, wherein said variable-area orifice includes a sliding member adapted to slide along the inner wall of said first chamber, and at least one communication hole of a communication passage is formed in the inner wall of said first chamber for establishing communication between said first chamber and said second chamber at the time of sliding of said sliding member, wherein said variable-area orifice includes an urging means to urge the sliding means away from the second chamber, and wherein the open area of said communication hole is increased when said sliding member slides toward said second chamber under the pressure of the fuel in said fuel discharge path against the force of said urging means.
Embodiments of the invention are explained below with reference to the accompanying drawings. In the drawings, similar or identical component members are designated by the same reference numerals, respectively. To facilitate understanding, the drawings are appropriately scaled.
When the injector 3 is turned off, i.e. when no fuel is injected from the injection port 36, the power supply to the piezoelectric element 21 is cut off by the electronic control unit ECU (not shown). Therefore, the piezoelectric element 21 cannot be displaced and the first piston 22a is urged upward by the spring 28. As a result, the valve body 23 is pushed up by the high-pressure fuel from the high-pressure path 34, and the leak port 29 is closed. Thus, the back pressure acting on the back pressure chamber 32 of the nozzle body 24 comes into equilibrium with the internal pressure of the high-pressure chamber 31, and the nozzle body 24 is pushed down by the spring 33 so that the forward end 37 of the nozzle body 24 closes the forward end hole 38 of the casing 39.
In the case where the injector 3 is in operation, i.e. in the case where fuel is being injected from the injection hole 36 as shown in
Referring to
Further, as shown in
The operation of the variable-area orifice 6 is explained below. As described above with reference to
According to this invention, the variable-area orifice 6 is arranged downstream of the confluences 59a to 59d where the branch pipes 52a to 52d from the injectors 3a to 3d are merged into the common fuel discharge path 55, and therefore the fuel is not supplied in one operation unlike in the prior art employing a check valve. Therefore, the pressure in the common discharge path is prevented from undergoing a sudden change. As a result, the pressure pulsation in the discharge path is reduced, and the variations in the amount of fuel injected from each injector is suppressed. Also, cavitation is prevented in the fuel return path 56, thereby reducing the erosion in the control valve chamber 27.
In
In
According to still another embodiment of the invention which is not shown, other urging means such as an electromagnetic solenoid or a piezoelectric actuator for urging the sliding member 70 may be employed in place of the spring 63 arranged in the second chamber 62. In this case, the position of the sliding member 70 can be controlled very accurately. This invention is not limited to the plurality of the embodiments described above with reference to the accompanying drawings, but any appropriate set of the embodiments described above is included in the scope of the invention.
Watanabe, Yoshimasa, Furukubo, Tatsumi
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